1. Field of the Invention
The present invention relates to a wavelength tunable laser.
2. Description of the Related Art
A wavelength tunable laser described in, for example, Japanese Unexamined Patent Application Publication No. 2004-336002 (hereinafter, referred to as document '002) has been known. The wavelength tunable laser described in document '002 includes an active layer having a gain, a distributed-feedback (DFB) area in which a sampled grating (SG) is formed, a distribution Bragg reflector (DBR) area in which a sampled grating is formed, and a phase control area. The sampling period of the sampled grating formed in the DBR area is different from the sampling period of the sampled grating formed in the DFB area.